JSFiddle - React, Tailwind, and code Playground

HTML

<input class="custom-file" data-num="4" data-onum="3" type="file" name="file[]" value=""/>

JavaScript

$( function(){
num= $(".custom-file").attr('data-onum');
console.log( num );
num= $(".custom-file").attr('data-num');
console.log( num );
});